How to get power from USB?

[Analyzer]

Hi,

I would like to get power from USB but i have some questions.

1.In USB port there are 4 pins.VCC,GND,D+,D-.Can i directly get power from VCC and GND? I will use 5V and 200 mA power.
2.This voltage will be a reference voltage and accuracy must be between 5.000 V ±0.120V ( 4.880 V ~ 5.120 V) Is usb port suitable for this?

Thanks in Advance.

Analyzer.

 

[Elavionic]

Go to this address. lots of usefull info about your request.
https://www.beyondlogic.org/usbnutshell/usb2.htm
I hope it help you.

 

[falling_stone]

Dear Analyzer,
You can draw up to 100mA before the device is configured and up to 500mA after the configuration is complete. If You just want to power something from the USB than as far as I understand, up to 100mA.
I would suggest You not to use USB power as a reference first, because of the voltage drop, which can be worse than Your requirements and second, because the USB power may be noisy. If this is an analog reference, up-convert USB power to a higher voltage with switching mode converter and then filter it out with linear regulator.
Best Wishes,
F.S.

 

[vsop]

Hi Analyzer,
1). u definitely r able to draw 200ma from usb port. the only exception is on the keyboard port of macintosh, as i know
2). vbus is noisy though, it's still usable & depending on how u filter, then make it clean. otherwise, how 2.0 bus powered device exist.

 

[Guest]

Hi Analyzer,
1). u definitely r able to draw 200ma from usb port. the only exception is on the keyboard port of macintosh, as i know
2). vbus is noisy though, it's still usable & depending on how u filter, then make it clean. otherwise, how 2.0 bus powered device exist.

/ User banned for copy/pasting posts just to get points. /

 

[Analyzer]

Hmm,
How can i filter it basicly? I mean i didnt leave space for this and i really need to drive power from usb

Analyzer.

 

[ME]

I don't think you can use the USB power for a ref. voltage with the spec. you require.
The USB voltage just isn't stable enough for this.

Maybe you can use a step up DC-DC converter followed by a resistor and 5.00 V voltage refernece + op. amp. buffer.

 

[Wizzard]

I would NOT recommend drawing that power without configuring the USB
because some computer will turn of the power to the port if the current exceeds the specified current in the enumeration
also USB specs is 4.25 volts to 5.25 most laptop will be at the lower end of this spec

/Wizzard

 

[Analyzer]

Hmm,
So i need to search a new stable voltage regulator.I will leave this port.

Analyzer

 

[Kripton2035]

2.This voltage will be a reference voltage and accuracy must be between 5.000 V ±0.120V ( 4.880 V ~ 5.120 V) Is usb port suitable for this?

Analyzer.

If you power your design with 5V, you should choose something lower for reference voltage like 4,096V or 2,5V. and use some voltage regulator (like maxim does max6250 or max6240) to handle this clean.